The normal rectal temperature of an adult horse is 37C-38.5C (99-101.5F), that of newborn foals tends to be a little higher at 37.5C-39C (99.5-102.2F) while that of donkeys is 36.5C-37.8C (97.2-100F). Rectal temperature is a useful parameter to measure when assessing your horse’s health. If you are unsure of how to take the temperature, be sure to ask your vet who will be able to advise you. Most people tend to use a standard digital thermometer available from any chemist shop.
Table of contents
What does an increased temperature mean?
When considering the cause of an increased rectal temperature, history is very important. If the horse has been exercising during high environmental temperatures, heat stroke is more likely. Whereas if they have a history of exposure to others with an infectious disease, then pyrexia due to a bacterial or viral cause may be more likely. However, a clinical examination by a vet may be necessary to determine the cause and to provide appropriate treatment.
In general, we can categorise a higher temperature as either pyrexia or hyperthermia. In the case of pyrexia, the body’s internal mechanism for regulating core temperature is reset to a higher level, usually in response to inflammation or infection. And in hyperthermia, the body’s ability to cope with excessive heat is overwhelmed, either due to excessive heat production or exposure, or both, and the body overheats. It is important to differentiate as treatment of these conditions is different. Antipyretic drugs for example, will not help in cases of heat stroke.
Pyrexia:
The list of possible causes of pyrexia is a lengthy one. It can be broken down into infectious or non-infectious causes. Your vet will need to ask you about your horse’s recent history as well as that of any horses yours has been in contact with, to start to narrow down this list to the most likely causes.
Some common infectious diseases include, Streptococcus equi equi (strangles), Equine influenza, Equine Herpes 1 or 4. Non-infectious causes include, peritonitis, pneumonia, colitis, endocarditis, or less commonly, neoplasia such as lymphoma. Immune mediated diseases can cause pyrexia but are quite rare.
Your vet will need to carry out a full clinical exam to look at every body system that may be affected. This may include blood samples to determine the white cell count; as well as to assess the overall state of health. Other tests that may be performed are ultrasonography of the chest and abdomen, abdominocentesis, to get a sample of fluid from the abdomen, or endoscopy to evaluate the respiratory system. The vet may also take samples to rule out infectious causes.
It is often difficult to ascertain the exact cause of pyrexia at the first visit, so you may need to wait for the results of laboratory tests. However, your vet will have narrowed down the list of possible causes and will be able to start some treatment. Initially, fluids and anti-pyretic medication are often given. Vets will not always prescribe antibiotics at the first visit, as they need to ensure that antibiotics are necessary and appropriate. Antibiotics will not help in viral infections and overuse may lead to antibiotic resistance.
Heat stroke:
Heat stroke is a very serious, potentially life-threatening illness. Clinical signs associated with heat stroke in addition to an increased body temperature, include, high heart rate, dullness, reluctance to drink or eat, reduced faecal and urinary output, and ataxia, or weakness and loss of coordination. Oher signs include an irregular heartbeat, flared nostrils, heavy breathing and very prominent veins in the skin.
Heat stroke most commonly occurs due to high intensity exercise in humid environmental conditions. However, it is important to remember that older horses are more vulnerable. And it is not unheard of for animals in a field without shade in the summer to succumb to heatstroke. So even if your horse is no longer an athlete, it does not mean that they are not still at risk. Animals with long hairy coats associated with Cushing’s disease can be more susceptible; as are the heavier breeds, overweight animals or those with dark hair colour. Some stables with poor ventilation can become extremely warm during the summer months. So sometimes being outside with shade and fresh water can be safer.
What should you do if you suspect heat stroke?
Call your vet immediately, your horse may need medical treatment such as intravenous or nasogastric fluids. Signs can progress very quickly. While waiting for the vet, it is important to do everything you can to cool the horse down. The most effective method is to use large volumes of cold water. Scraping the water off is unnecessary, the best thing is to keep pouring the water. Fans or a cool breeze will help, so get them out of a stable if possible. Ice packs and damp rugs are less effective than plain, cold water.
Remember, you cannot cool a horse too quickly and cold water will not increase the risk of colic or other illnesses.
If your horse becomes very agitated at the water, stop briefly, but try to continue as soon as they are calmer.
Offer the horse water to drink. Electrolytes will help; but always offer plain water in addition to electrolyte infused water as some horses do not like the taste of electrolytes. Water without electrolytes is preferable to water that they refuse. Cold water is safe to drink, but some horses prefer warm or room temperature water.
In summary, overheating is dangerous to horses
It is always advisable to have a thermometer as part of your yard first aid kit, along with normal reference ranges if you are unsure. Taking your horse’s temperature when they are fit and healthy will give you an idea of what is normal for them. It is advisable to check the battery occasionally or have a backup particularly if you don’t use the thermometer often; it might fail just when you need it most. If your horse does have a high temperature, call your vet for advice and an examination. And if you think your horse is suffering from heatstroke, start cooling them immediately. If you suspect that your horse may have an infectious disease, remember to keep them isolated from others while you are waiting for your vet.
Discussion